Approximately one million cases of gonococcal infections will have occurred by the end of 1990 and based on current trends, it is likely that gonorrhea will remain a prevalent sexually transmitted disease for the next several years. This research program addresses the role of the human neutrophil in host defense against invading gonococci. We seek to understand how gonococci are killed by phagocytes in vitro so as to learn how they apparently develop resistance to killing during infection. Earlier studies showed that the nonoxidative antimicrobial capacity of lysosomal cathepsin G is an important determinant of phagocyte bactericidal action. We have identified different chromosomal mutations that modulate levels of gonococcal susceptibility to cathepsin G and a synthetic antibacterial peptide derived from its sequence. Expression of these mutations results in hypersusceptibility of gonococci to cathepsin G by effecting either the binding of the bactericidal protein to the gonococcal surface or by altering an enzyme that complete peptidoglycan synthesis tat cell division. This enzyme is termed penicillin binding protein 2 (PBP 2) and it gives evidence of being the lethal target of cathepsin G action. Gonococcal susceptibility to cathepsin G is augmented by a mutation which increases the amount of a highly conserved, invariant 44 kDa outer membrane protein (OMP). Over-expression of this OMP also results in increased resistance of gonococci to several hydrophobic, clinically useful antibiotics. This OMP also gives evidence of being the major penicillin in binding protein (PBP 3) in gonococci. Two major goals of the current proposal are to define the sequence of this OMP and to ascertain how its synthesis is regulated. Determining the mechanism by which gonococci are killed by cathepsin G is the third goal of the proposal. Past studies suggest that cathepsin G is third goal of the proposal. Past studies suggest that cathepsin G forms a complex with PBP 2, a periplasmic protein anchored to the cytoplasmic membrane. Using isogenic strains that differ in levels of susceptibility to cathepsin G and contemporary techniques in molecular biology and genetics, experiments will be conducted to determine susceptibility also increase gonococcal resistance to antibiotics, the results will advance our knowledge regarding the mechanisms by which gonococci have evolved resistance to clinically useful antimicrobial agents.